It’s all smiles now for Finn (Shue) and Russell (Ted Danson), but that wasn’t always the case. (
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Let’s get one thing straight, right off the blood-spattered baseball bat: Elisabeth Shue is not Marg Helgenberger’s replacement on “CSI.”

Shue, who made her debut last week as blood spatter expert Julie “Finn” Finlay, is horrified by the notion that fans might think that could be the case.

“How do you replace somebody who’s done something for so many years?” she says, sounding aghast.

“I feel like there’s a space left open for somebody to come in and join the group, but I really don’t feel like I’m replacing her.”

The producers have underscored Shue’s feeling by introducing her character as an experienced CSI, but not management-level material like Helgenberger’s Catherine Willows, who quit the lab for happier FBI pastures last month.

And, Finn won’t be the mother hen of the group, either.

Turns out she worked — closely — with the zany D.B. Russell (Ted Danson) before he transferred to the Las Vegas crime lab at the beginning of the season.

“We might’ve even had a history, shall we say, before he got so happily married,” says Shue, 48.

“There is the possibility that we might’ve known each other intimately and that could have [be] the reason why he fired me when I worked with him back in Seattle.

“When you first meet Finn, there’s a little bit of mistrust between us. There’s a lot of past history that, as [the season] has been going on, is getting more fun” to work on.

Originally the character was meant to be an anger management devotee. But, Shue cajoled the writers into easing up on the anger issue.

“I have to say that that’s not part of my authentic personality,” Shue admits. “I talked about many other ways that I would manipulate [situations], step over boundaries and do things that are inappropriate that don’t necessarily involve anger.

“They were like, ‘Oh, that’s great!’ They want to make [the character] as tailored to you as they can.”

After a month on set, the only thing that Shue hasn’t yet convinced the writers to do is to let her beat up some bad guys — even though she asks pretty much every week.

“I’m very excited to get my gun,” she says. “I’m hoping that some havoc will happen and I’ll have to go in there and physically take care of people. That’s part of the job that I’m really excited for — I haven’t really been able to play a character where I’ve been really physical, so I’m hoping that I get to do that.”

Another new experience: participating in autospy scenes. “I kept opening up the [fake] body and looking at all the apparatus,” she says. “The intestines and what they felt like, where’s the heart, lift up the ribs — it’s amazing how realistic the bodies they make for the show are.”

To “surround myself with the reality of what the life is,” Shue visited the Los Angeles coroner’s office and crime lab.

“I’ll never forget it for the rest of my life,” she says. “It’s profoundly terrifying, to the point where it became inspiring…they must really value life, because if you’re around that kind of death every single day, I’m sure it makes you grateful that you’re alive.”

Shue’s return to series TV after a nearly 30-year hiatus — in 1984 she starred in ABC’s military drama “Call to Glory” — was a matter of good timing and family connections.

Thanks to her husband, director/producer Davis Guggenheim, Shue had an in with “CSI” exec Carol Mendelsohn, who co-produced the ill-fated CBS series “The Defenders” with him.

Meanwhile, “the timing was just perfect” for the job offer, says Shue, mom to three kids, Miles, 14, Stella, 10 and Agnes, 5. “My littlest just went to kindergarten, so I wasn’t going to be so desperate to be with her constantly. I thought, ‘Maybe I should take a risk and go out there and see what it’s like.’ ”

“It happened so fast. I think that’s why it was a good way for it to happen,” Shue says, adding that “I didn’t have time to over-think it.”

Not entirely surprising, considering that, a decade ago, Shue went back to Harvard — she’d originally transferred there after two years at Wellesley College — to finish her bachelor’s degree, living off campus in Cambridge with then two-year-old Miles.

“I had just one semester” left, she says, “So I took the hardest courses.Finally, at age 37, I was the perfect college nerd; it was really, really fun.”

Over the past nine years, Shue, who was nominated for a Best Actress Oscar in 1995 for her harrowing performance in “Leaving Las Vegas,” has kept a relatively low acting profile — on purpose. “I’ve done just one movie a year,” she says, “Maybe nobody’s ever seen them, but I’ve still been stimulated and artistically challenged and I’ve really been able to be hands-on mom.”

A good thing, too, since she’s based part of her portrayal of Finn on her five-year-old daughter, “who is so impulsive and so right about everything.”

“I swear I feel like I’m just tasting the moment of confidence, at age 48, that she inhabits at age 5,” Shue says.

“I watch her all the time and I feel like her essence is what I want Finn to be — slightly mischievous and young in the way she approaches her science and her job, that there’s a part of her that loves the cops and robbers part of the job, and sometimes gets lost in the adrenaline rush of what it’s like to be out there, solving crimes.”